Author/Editor		Kreft, M; Kuster, V; Grilc, S; Rupnik, M; Milisav, I; Zorec, R
Title		Synaptotagmin I increase the probability of vesicle fusion at low (Ca2+) in pituitary cells
Type		članek
Source		Am J Physiol, Cell Physiol
Vol. and No.		Letnik 284
Publication year		2003
Volume		str. C547-54
Language		eng
Abstract		Synaptotagmin (Syt I), a low-affinity Ca2+ -binding protein, is thought to serve as the Ca2+ sensor in the release of neurotransmitter. However, functional studies on the calyx of Held synapse revealed that the rapid release of neurotransmitter requires only approximately micromolar [Ca2+], suggesting that Syt I may play a more complex role in determining the high-affinity Ca2+ dependence of exocytosis. Here we tested this hypothesis by studying pituitary cells, which possess high- and low-affinity Ca2+ -dependent exocytic pathways and express Syt I. Using patch-clamp capacitance measurements to monitor secretion and the acute antisense deletion of Syt I from differentiated cells, we have shown that the rapid and the most Ca2+ sensitive pathway of exocytosis in rat melanotrophs requires Syt I. Furthermore, stimulation of the Ca2+ -dependent exocytosis by cytosol dialysis with solutions containing 1 micro M [Ca2+] was completely abolished in the absence of Syt I. Similar results were obtained by the preinjection of antibodies against the CAPS (Ca2+ -dependent activator protein for secretion) protein. These results indicate that synaptotagmin I and CAPS proteins increase the probability of vesicle fusion at low cytosolic [Ca2+].
Descriptors		PITUITARY GLAND EXOCYTOSIS CALCIUM CALCIUM-BINDING PROTEINS RATS, WISTAR PATCH-CLAMP TECHNIQUES RNA, MESSENGER POLYMERASE CHAIN REACTION HIPPOCAMPUS CEREBELLUM SPINAL CORD MICROSCOPY, CONFOCAL